The rapid growth of microfluidic technologies in the last several decades has led to the development of various degrees of micro total analysis systems. Specifically, the application of microfluidic technologies to the field of cell biology have enabled the development of integrated “lab on a chip” systems that are capable of integrating multiple laboratory steps on to a single device. An important cell manipulation process that needs to be integrated into a “lab on a chip” system is the ability to switch cells of interest to multiple downstream processes for further analysis.
Multiple microfluidic switches for particles and cells have been developed including electro-osmotic flow (EOF), dielectrophoresis, microfabricated valves, external valves and optical tweezers. These microfluidic switches were later utilized in integrated micro Fluorescence Activated Cell Sorting (μFACS) systems. However, many of the current microfluidic switches have several drawbacks such as low throughput, low cell recovery, complex off-chip optical tweezer or pneumatic valves setup and high voltages (kV).
Recently, there has been increasing interest in utilizing acoustically excited bubbles within microchannels as simple on-chip actuator systems for applications in pumping, mixing and trapping. Specifically, Lateral Cavity Acoustic Transducers (LCATs) are simple on-chip actuators that are easily fabricated and can be actuated using a battery operated portable electronics platform. LCATs are dead-end side channels that are in the same plane as the microchannels themselves requiring no additional fabrication steps other than those needed to produce the single layer device. When the device is filled with liquid, LCATs trap bubbles creating an air-liquid interface that can be excited using an external acoustic source such as a piezoelectric transducer.
Patel et al. demonstrated the potential application of LCATs for particle and cell sorting applications. See Patel et al., Thirteenth International Conference on Miniaturized Systems for Chemistry and Life Sciences November 1-5, μTAS, Jeju, Korea (2009). In the device disclosed in Patel et al., the LCAT is positioned upstream of the outlet junctions. This configuration produced instabilities in the air/liquid oscillations and required higher voltages in order to generate particular patterns of streaming.